Process for extracting animal glue in concentrated aqueous solutions



EXTRACTED GLUE IN AQUEOUS PHASE fi g' l LOW SPECIFIC GRAVITY WATER- IMMICIBLE ORGANIC SOLVENT GLUE STOCK SOLIDS /PERFORATED PLATE OR FINE SCREEN J SPENT STEAM May 22, 1956 A. L. L

PROCESS FOR EXTRACTING ANIMAL GLUE III CONCENTRATED AQUEOUS SOLUTIONS Filed April 27, 1953 LIVE STEAM f4 STEAM JACKET T q a U o g (I Q Mai U i Q v o W EXTRACTED GLUE IN AQUEOUS PHASE CONCENTRATED EXTRACTED GLU E CONCENTRATED EXTRACTED GLU E HIGH SPECIFIC GRAVITY WATER- IMMICI BLE ORGANIC SOLVENT LIVE STEAM rzZZ -GLUE STOCK SOLIDS "STEAM JACKET SPENT STEAM INI 'EN TOR.

PROCESS FOR EXTRACTING ANIMAL GLUE m CON CENTRATED AQUEOUS SOLUTIONS August L. Lolli, Chicago, Ill., assignor to Armour and Company, Chicago, 111., a corporation of Illinois Application April 27, 1953, Serial No. 351,409

(Ilaims. (Cl. 260-118) This invention relates to a process for extracting animal glue in concentrated aqueous solutions.

The presently employed industrial method for the extraction of animal glue involves the heating of conditioned glue stock in a Water bath to extract the glue. The extracted glue mixe with the water of the bath, resulting in a dilute aqueous solution of glue, which must subsequently be concentrated by the removal of large quantities of water to prepare the final dry glue product. In other words, the dilute aqueous solution of glue is concentrated until the glue solution has sufiiciently high solids content to gel. The usual solids content of the extracted glue before concentration ranges from about 3 to 6%, while usually a solids content of at least 10 to is required to gel the glue, and sometimes a solids content of up to may be necessary to produce a gel.

Various methods have heretofore been used for removing the water in the glue concentration step, but all of them require expensive drying equipment, such as multiple effect evaporators, and require the handling of large volumes of the glue solutions with a consequent large expenditure of time and money. Therefore, it has long been desired to provide a method for extracting and preparing animal glue which eliminated or subsequently reduced the amount of concentration required.

The solution to the problem just discussed has been complicated by the desire to completely extract the glue from the glue stock in the shortest possible period of time. More specifically, the obvious answer of using less water in the extraction bath in relation to the glue stock solids so as to thereby obtain a more concentrated glue solution has not heretofore proven feasible because of the increased difiiculty of extracting the glue. This can readily be appreciated when it is realized that present practice frequently involves a series of four to six extractions or cooks, each lasting from five to six hours and progressing from a starting temperature of 65 C. for the first cook to boiling for the last cook. Further, a dilute solution of glue is obtained in each of the cooks.

Another complicating factor is that attempts to extract glue in more concentrated solutions have frequently resulted in an impairment of either the gel strength, viscosity, or both. This is particularly true where the extraction is being carried out at an acid pH.

It is therefore a general object of this invention to provide for the first time a commercially feasible process for extracting animal glue in concentrated aqueous solutions. More specifically, it is an object of this invention to provide a process for extracting animal glue in solutions of such concentrations that they can be gelled without further concentration, thus eliminating or substantially reducing the amount of drying heretofore required. Another object of this invention is to provide a process of the character described which also results in a reduction in the time heretofore required to complete extraction of the glue from the glue stock, while at the same time producing a glue having an exceptionally high gel strength and viscosity, even when the glue is being extracted under 2,745,949 Patented May 22, 1956 ice acidic conditions. Further objects and advantages will appear as the specification proceeds.

The method of this invention is illustrated in the accompanying drawing, in which- Figure 1 shows somewhat diagrammatically a preferred embodiment of the method and Fig. 2 shows an alternate embodiment.

In one of its aspects this invention involves a method of extracting animal glue which is characterized by the step of cooking out a concentrated aqueous solution of glue by contacting conditioned, water-impregnated animal glue stock solids with an essentially water-immiscible heat transfer medium in liquid form maintained at a glue-liberating temperature. In other words, as distin guished from previous procedures, in the method of this invention the only water present during the extraction is that which is intimately associated with and has been taken up by the glue stock solids and the water-swollen solids are immersed in a bath composed of a waterimmiscible liquid medium, which has the property of transferring heat to the solids and thereby cooking out a concentrated aqueous solution of glue, which does not mix with the heat transfer medium because of its waterimmiscible character.

Any conditioned water-impregnated glue stock can be treated according to the method of this invention, but the method is preferably carried out with hide glue stock which has been conditioned by any of the known procedures, such as liming, etc., and has become swollen with water. In the conventional process wherein hide glue stock, such as hide trimmings, etc., is soaked in a saturated lime solution for a period of from to days, and the conditioned glue stock is soaked in water having acidic pH to remove lime and calcium salts, the glue stock is then washed back to approximately a neutral pH value, or neutralized with an alkaline reagent before being extracted with hot water. This method may cause the hide glue stock to swell at least 100% with water, and this is satisfactory for the purposes of this invention. However, it is preferred to employ glue stock which has been swollen to the maximum amount possible by treating it with an aqueous acidic solution. For example, conditioned glue stock can be soaked in Water at a pH from 1.5 to 3.5 to swell the hides, and then extracted without complete neutralization, that is, at a pH below 6.5 and preferably at a pH from 1.5 to 6.0. This procedure will greatly increase the amount of water taken up and retained by the glue stock, and in many cases the glue stock may be swollen 200% or more with water. It will be understood, of course, that other methods of conditioning and impregnating the glue stock with water can be employed, such as the combined microorganism and acid-treating method described in co-pending application, United States Serial No. 339,166, filed February 26, 1953. A procedure for acid-treating glue stock such as hide trimmings to produce maximum swelling of the glue stock is described in co-pending application, United States Serial No. 243,378, filed August 23, 1951.

For reasons which will subsequently become apparent, the method of this invention is also particularly adapted for use in extracting glue from glue stocks containing both collagen and fat. In fact, it has been found that the presence of large amounts of fat in the glue stock is not particularly objectionable as in prior aqueous extraction procedures, when the preferred method of this invention is employed, wherein a water-immiscible organic fat solvent is used as the heat transfer medium. By way of example, chlorinated hydrocarbons of less than three carbon atoms, such as ethylene dichloride, carbon tetrachloride, chloroform, etc. can be used as the heat transfer medium. Good results are also obtained with petroleum 3 fat solvents like kerosene. Another preferred class of solvents is the triglycerides of fatty acids, especially animal fat of the same kind as in the glue stock. For the purpose of this invention, such fatty acid triglycerides can be regarded as water-immiscible organic fat solvents. Of all the heat transfer mediums tested, perhaps the best results are achieved with ethylene dichloride, although satisfactory results have been obtained, as indicated, with many other specific solvents, such as kerosene, benzene, toluene, carbon tetrachloride, chloroform, oleo oil, animal fat, mineral oil, lubricating oil, etc. Apparently, a principal requirement is that the water-immiscible liquid shall have the property of transferring heat to the glue stock and displacing or forcing the glue out of the tissue.

As might be suspected, there will be some differences in the method of practicing the invention when heat transfer mediums which are lighter than water are em ployed as compared when the heat transfer medium is heavier than water. However, either heat transfer mediums of greater or lesser specific gravity than water can be used, as illustrated in Figs. 1 and 2 of the drawing. Looking first at Fig. 1, there is shown somewhat diagrammatically a typical set-up for a batch extraction according to the method of this invention when the waterimmiscible solvent is of low specific gravity, that is, when it is lighter than water, and will float on water. The extraction vessel has a bottom which tapers to a valve-controlled outlet 11 and has its intermediate portion divided with a perforated plate 12 above which are maintained the glue stock solids 13 suspended within the water-immiscible heat transfer medium 14. As illustrated, a heating jacket 15 is provided around the upper portion of vessel 10 and appropriate connections are provided for introducing and removing steam to jacket 15. As the heat is transferred to the glue stock solids by the heat transfer medium 14, a concentrated aqueous solution of glue is forced out of the solids and settles downwardly to collect in a pool 16 adjacent outlet 11. The extracted glue in pool 16 can then be continuously or intermittently drawn off through outlet 11 as illustrated.

Fig. 2 shows a modified batch extraction set-up which might be employed when the heat transfer medium is of high specific gravity, that is, when it is heavier than water. As illustrated, extraction vessel 20 is provided intermediately with a perforated plate 21 beneath which the glue stock solids 22 are introduced through inlet 23 and finally withdrawn through outlet 24. A lower portion of vessel 20 is provided with a steam jacket 25, which has appropriate steam inlet and outlet connections as illustrated, and the upper portion vessel 20 has a restricted neck 26 which is provided with an outlet 27. In this embodiment, the concentrated aqueous solution of glue rises to the top of the water-immiscible heat transfer medium 28 and collects in pool 29 which can then be Withdrawn through outlet 27 as desired. While this method of operation is quite feasible, it is not as convenient as the method illustrated in Fig. l, and therefore the use of water-immiscible organic solvents or more generally heat transfer mediums which are lighter than water is preferred.

As illustrated above, with the method of this invention it is possible to decrease the extraction time required for complete extraction of the glue, although the amount of glue which can be extracted in a single run is related to the amount of water which has been absorbed by the glue stock. For example, glue stock which has been swollen in acid permits the extraction of up to 65% of the available glue in three to four hours at 55 C. When the water in the glue stock has been exhausted, the partially-extracted glue stock can be separated from the heat transfer medium and further processed to obtain the rest of the glue. For example, this can be done by a conventional water extraction of the residual glue, or

the glue stock can be reswollen (replumped) and a further extraction carried out as already described using the method of this invention? it has been found that glue can be extracted by the use of water-immiscible heat transfer mediums at considerably lower temperatures than in conventional water extractions, where the extraction temperatures generally start at about C. When using water-immiscible heat transfer mediums, useful extractions can be made down to temperatures as low as 37 0., although optimum results appear to be obtained at temperatures around 55 C. However, much higher temperatures can be employed if desired to speed up the extraction without harmful effect, because the extracted glue can be rapidly removed from the heated extraction zone, thereby tending to limit the degree of hydrolysis even though temperatures of 100 C. or above are employed.

At present hide glues which have gel strengths rang ing from 400 to 500 and correspondingly balanced viscosities of about 200 are regarded as topgrade glues. With the method of this invention as described, glues of this quality can be readily produced from hide glue stock, and in addition glues can be produced which have gel strengths and viscosities much higher than has heretofore been possible on a commercial scale. This invention is further illustrated by the following specific examples:

Example I Lime-conditioned and acid-treated hide pieces were extracted in ethylene dichloride in the presence of calcium carbonate at 72 C. to obtain a concentrated aqueous solution of glue which gelled without further concentration to produce a glue having a gel strength of 515, a viscosity of 132, and a pH of 6.7.

Example II A further run was made as described in Example I, except that calcium carbonate was not employed as a neutralizing agent and the extraction temperature was 60 C. The extracted glue thus obtained had a gel strength of 810, a viscosity of 220, and a pH of 3.8.

Example Ill Acid-conditioned water-swollen pigskin was extracted in ethylene dichloride at C. The concentrated glue solution obtained gelled without further concentration to produce a glue having a gel strength of 750, a viscosity of 297, and a pH of 5.4.

Example IV Lime-conditioned hide pieces were cooked in ethylene dichloride at 65 C. to directly produce a glue having gel strength of 811, a viscosity of 416, and a pH of 6.7.

Example V Lime-conditioned acid-treated beef tendons were extracted at C. in ethylene dichloride. The glue thus obtained had a gel strength of 650, a viscosity of 450, and a pH of 5.0.

Example VI Lime-conditioned acid-treated hide pieces were heated at 65 C. in toluene in the presence of calcium carbonate as a neutralizing agent. The concentrated aqueous solution in glue gelled without further concentration to produce a glue having a gel strength of 551, a viscosity of 165, and apl-I of 5.5.

Example VII A further run was made with the glue stock of Example VI using kerosene as the heat transfer medium and maintaining the kerosene at 60 C. Calcium carbonate was again used as the neutralizing agent. The glue obtained had a gel strength of 636, a viscosity of 170, and a pH of 7.3.

Example VIII Another run was made with a glue stock of Examples VI and VII, using beef fat as the heat transfer medium. The temperature employed was 65 C. and calcium carbonate was used as a neutralizing agent. The glue produced had a gel strength of 855, a viscosity of 197, and a pH of 6.7.

Example IX pounds of conditioned acid-plumped hide glue stock was cooked in ethylene dichloride in the presence of calcium carbonate for seven hours. This resulted in an extraction of 59.7% of the available glue, and the glue obtained had a viscosity of 221 and a gel strength of 810. The partially-extracted glue stock was then replumped by treating it with water at an acidic pH. The replumped glue stock was again cooked in ethylene dichloride in the presence of calcium carbonate. At the end of four hours an additional 30.5% of the glue had been extracted, and the extracted glue was found to have a viscosity of 139 and a gel strength of 656. The glue stock residue was then cooked in water for three hours to yield an additional 9.8% of glue having a viscosity of 85 and a gel strength of 205.

While in the foregoing specification the method of this invention has been described in relation to certain preferred embodiments and specific details thereof have been set forth, it is apparent to those skilled in the art the method of this invention is susceptible to other embodiments and that many of the details set forth can be varied widely without departing from the spirit of the invention.

I claim:

1. In a method of extracting animal glue, wherein animal glue stock solids are conditioned and wherein the conditioned glue stock solids are soaked in an aqueous acidic solution to obtain acid-swollen glue stock solids, the steps of contacting said acid-swollen glue stock solids with an essentially water-immiscible organic fat solvent in the absence of water other than that impregnated in said glue stock solids, said organic fat solvent being maintained at a glue-liberating temperature to cook out a concentrated aqueous solution of glue, and separating said concentrated aqueous solution of glue from residual glue stock solids.

2. The method of claim 1 in which said organic fat solvent is a chlorinated hydrocarbon containing less than 3 carbon atoms.

3. The method of claim 2 in which said chlorinated hydrocarbon is ethylene dichloride.

4. The method of claim 1 in which said organic fat solvent consists of fatty acid triglycerides.

5. The method of claim 1 in which said organic fat solvent consists of animal fat of the same kind as in the glue stock.

6. In a method of extracting animal glue, wherein hide glue stock is conditioned and wherein the conditioned hide glue stock is soaked in water having a pH below 6.5 to obtain a glue stock swollen at least 100%, the steps of heating the acid-swollen glue stock in an essentially water-immiscible organic fat solvent in the absence of Water other than that impregnated in said glue stock, said organic fat solvent being maintained at a glue-liberating temperature above 37 C. to cook out a concentrated aqueous solution of glue, and separating said concentrated aqueous solution of glue from residual glue stock.

7. The method of claim 6 in which said organic fat solvent is of lower specific gravity than water, said method being characterized by the further step of removing said concentrated aqueous solution of glue from beneath said organic fat solvent.

8. The method of claim 6 in which said organic fat solvent is of higher specific gravity than water, said method being characterized by the further step of removing said concentrated aqueous solution of glue from above said organic fat solvent.

9. In a method of extracting animal glue, wherein hide glue stock is conditioned and wherein the conditioned hide glue stock is soaked in water having a pH of from 1.5 to 3.5 to obtain glue stock swollen at least 100%, the steps of heating the acid-swollen glue stock in a Waterimmiscible organic fat solvent in the absence of water other than that impregnated in said glue stock, said organic fat solvent being maintained at a glue-liberating temperature of at least C. to cook out a concentrated aqueous solution of glue, and separating said concentrated aqueous solution of glue from residual glue stock.

10. In a method of extracting animal glue, wherein animal glue stock solids are conditioned and wherein the conditioned glue stock solids are soaked in an aqueous acidic solution to obtain acid-swollen glue stock solids, the steps of contacting said acid-swollen glue stock solids with an essentially water-immiscible organic fat solvent in the absence of water other than that impregnated in said glue stock solids, said organic fat solvent being maintained at a glue-liberating temperature until a portion of the glue has been cooked out as a concentrated aqueous solution of glue, separating the partially extracted glue stock solids from the organic fat solvent, replumping the separated glue stock solids by soaking in an aqueous acidic solution, then contacting the replumped glue solids with an essentially water-immiscible organic fat solvent in the absence of water other than that impregnated in said replumped glue solids, said organic fat solvent being maintained at a glue-liberating temperature to cook out another portion of the glue as a concentrated aqueous solution of glue, and separating said concentrated aqueous solution of glue from residual glue stock solids.

References Cited in the file of this patent UNITED STATES PATENTS 89,709 T uttle et a1 May 4, 1869 2,301,242 Billaudot Nov. 10, 1942 2,562,221 Tour July 31, 1951 FOREIGN PATENTS 181,865 Great Britain June 29, 1922 

1. IN A MEHTOD OF EXTRACTING ANIMAL GLUE, WHEREIN ANIMAL GLUE STOCK SOLIDS ARE CONDITIONED AND WHEREIN THE CONDITIONED GLUE STOCK SOLIDS ARE SOAKED IN AN AQUEOUS ACIDIC SOLUTION TO OBTAIN ACID-SWOLLEN GLUE STOCK SOLIDS, THE STEPS OF CONTACTING SAID ACID-SWOLLEN GLUE STOCK SOLIDS WITH AN ESSENTIALLY WATER-IMMISCIBLE ORGANIC FAT SOLVENT IN THE ABSENCE OF WATER OTHER THAN THAT IMPREGNATED IN SAID GLUE STOCK SOLIDS, SAID ORGANIC FAT SOLVENT BEING MAINTAINED AT A GLUE-LIBERATING TEMPERATURE TO COOK OUT A CONCENTRATED AQUEOUS SOLUTION OF GLUE, AND SEPARATING SAID CONCENTRATED AQUEOUS SOLUTION OF GLUE FROM RESIDUAL GLUE STOCK SOLIDS. 